(1) Field of the Invention
The present invention relates in general to time domain multiple access (TDMA) mobile communication systems.
(2) Description of Related Art
One standard for mobile communication is the global system for mobile communication (GSM) which is a widely used form of TDMA digital wireless telephony technology. Being a mobile system, power consumption is of primary concern since batteries are heavy and expensive. Further, if power drain is high, use of the mobile telephone will be limited by battery life. Clearly, it is desirable to minimize power consumption in mobile communication applications.
One way of limiting power drain is by minimizing the amount of time the receiver section is powered especially since transmissions in TDMA based systems are received in spaced bursts of information. As will be appreciated, timely application of power to the receiver section of the mobile unit is highly dependent on remaining closely synchronized with the transmission rate of the base station. Such synchronization is even more critical as the mobile unit roams from one base station to another. Accordingly, GSM systems rely on extracting the timing information required for synchronization with the base station during an active call from the burst. Mobile needs to obtain this information with accuracy of 1/8 th of a bit to ensure synchronization with the base station.
Traditionally, a software implemented finite impulse response (FIR) filter is used to locate the position of such signal. Typically, the FIR filter will have a large number of taps. e.g., ninety-six or more taps in order to ensure the necessary accuracy in recovering the timing information with desired accuracy. However, it will be appreciated that software filtering is computationally demanding in terms of compute time, system resources (for example, each tap coefficient must be stored together with intermediate calculated values) and power drain.
By way of example, in a ninety-six tap FIR filter, the filtering process will perform 96 multiply and accumulate operations on every sample. And since the signal must be filtered in real time, the processor must be fast enough to fully execute the filter process. It being well known that power consumption increases as the operating rate of the processor increases since power is proportional to switching activity.
Although it is possible to improve timing resolution by over-sampling the burst signal and rapidly processing the signal within the GSM frame rate, it will be appreciated that processors operating at a clock rate sufficient to process will have high power consumption.